A rivalry is reportedly brewing on the set of Gossip Girl over two of the show’s stars’ musical ambitions. Taylor Momsen is said to be upset that the show has thrown its support behind co-star Leighton Meester’s singing career instead of hers. “Taylor is not happy that Gossip Girl has been playing Leighton’s music on the show, and they have never asked to play any of her songs,” a source tells HollywoodLife.com. “It’s creating a lot of tension on set.” When pressed for comment, a rep for the show’s network, the CW, doesn’t mince words: “The show will support Taylor and her music when the time is right, but her music is not ready yet.”